Different HDTV signals?

Yes ESPN looks terrible except when they are truly broadcasting a game with High Def Camera's . From what I understand Fox , even when say showing a football game in widescreen , is not true high def, however they are upgrading , and should be full blown high def capable this year. Your right ESPN actually uses widescreen even when not broadcasting in high def , its just a stretched standard def picture. But , all minor issues , that eventually will pass. Hi Def when done properly is great !

Yes The above is correct, when the program is broadcast in standard definition, you will see bars all around your screen, when they are broadcasting in High def, you will view it in widescreen. Perfectly normal. If you are not getting any widescreen broadcasts during primetime your cable company is not transmiting them in the High Def format. If some of the time on the networks you are getting widescreen , thats because some shows like NYPD Blue are produced in high def, while a show like Friends is not.
Also many cable companies with high Def capability broadcast the networks in High def on different channels on your cable box , For example CBS is channel 2 in NY/NJ but if I want to view it in high def on my system it is channel 183.

If you are watching Boxing on HBO or Showtime and it is in a 4:3 Format, it is not in high definition.